The present invention relates to improvements for making fiber reinforced compound material and more particularly the invention relates to improvements about monitoring the integrity of such parts under utilization of embedded light wave conductors and optical filaments. The invention relates specifically to the external accessability of such light conductor fibers being embedded for purposes of monitoring the development of cracks in the fiber reinforced compound material.
Generally speaking it is known to embed light conductor fibers in structural materials including particularly fiber reinforced compound materials and to inspect whether or not light is conducted adequately and umimpeded through the fiber optic, under the assumption that in the case a crack develops the optical path will be interrupted. Obviously prior to such a response the optical fiber element must be without impairment as to its capability of conducting light. Devices of this type are for example disclosed in U.S. Pat. Nos. 4,772,092, 4,629,318 and others listed in the latter patents.
It was found however that the external accessability of such fibers i.e. their projection from the parts in which most of the fibers are embedded presents problems since these delicate indicators impede the processing and working of the construction part unless special steps are taken to protect the external portion of the light conducting fiber. Moreover, it has to be considered that e.g. the construction part needs curing when otherwise is assembled including the embedment of the light conducting fiber and the curing may require exposure to high pressure and/or high temperature in an autoclave. Again it is obvious that the optical element must not be damaged by this procedure. It was found, however, that special protection is needed. Otherwise the integrity of the crack monitor is not guaranteed.